The need exists for wood filler compositions that are capable of adhering to a variety of substrate types, including treated wood and untreated wood. Wood fillers are used in the construction and furniture industries to repair soft or hard wood or wood products, and also by contractors and do-it-yourself consumers to repair or cure imperfections in furniture or woodwork, often where the wood has been cracked or otherwise been damaged. It is desirable that wood be able to maintain its natural beauty, such as when wood is stained to show the grain. It must not be readily apparent that a filler has been applied to the wood. It is therefore important that the filler be able to be smoothed even with the wood surface. It is also desirable that the wood filler remain adhered to the wood, whether the wood is natural, painted, or stained.
There are several beneficial characteristics to be achieved in a wood filler product. The wood filler should be easily spreadable, and should spread without the filler breaking up as it is spread. A wood filler also most advantageously has a sufficiently long working time to allow the wood filler to be worked into a desired form or surface before setting. It is also desirable to produce a wood filler that also has a relatively short setting time, so that the wood filler sets to a point where it can be sanded or otherwise finished in a relatively short period of time. In this regard, it is also beneficial to produce a wood filler that may be sanded without clogging the sand paper or other abrading media (that may reduce its efficacy). It is also beneficial to produce a wood filler that does not shrink or crack upon drying. Another beneficial characteristic in a wood filler is to have a relatively low post-drying density which bears a relation to the ability of the filler resist cracking or shrinking upon drying. It is also desirable that the wood filler have uniform staining characteristics, to resist over-staining or under-staining.
Various wood fillers are available in the art, and generally utilize waterborne technology or solvent-borne technology. Although solvent-borne technologies form a surface skin more rapidly than waterborne technologies, the interior part of the product still is heavily filled with either a flammable solvent or water which prevents or restricts the product from complete internal setting/solidification. Upon drying, conventional wood fillers are also subject to volume shrinkage due to the solvent or water that evaporates as the product sets. This effect may reduce the total strength of a repaired area. Hot melt adhesive technology provides rapid “through cure” as the product cools from a molten state to a fixed, room temperature state; however, such materials lack important wood filler properties such as ease of sandability and stainability. Therefore, there is an ongoing need for an effective wood product that does not suffer from these deficiencies.
The use of cellulose-containing compounds in wood fillers is known in the art. As described in U.S. Pat. No. 1,947,438, a cellulose ester, specifically nitrocellulose, was used in a wood filler composition. Wood filler compositions containing a cellulose ester that are known in the art rely on rosin esters, resins, or gums as tackifiers. The composition containing cellulose acetate described in U.S. Pat. No. 1,947,438 includes 100 parts cellulose acetate, 5 parts triphenyl phosphate, 15 parts paraethyltoluenesulphonamide, 5 parts dibutyl tartrate, 35 parts dimethyl phthalate, 35 parts ester gum, 250 parts wood flour, and 600 parts volatile solvent. However, these wood filler compositions suffer from low adhesion on certain substrates.
U.S. Pat. No. 6,036,761 also a solvent based wood filler comprising an organic solvent component, nitrocellulose, calcium carbonate, a filler selected from aluminum silicate and magnesium silicate and mixtures thereof, and wood flour.
Although cellulose nitrate, also referred to as nitrocellulose, dries quickly and has other benefits, it also has a significant limitation because it is a highly flammable compound. Because of this flammability (and explosiveness), there is a commercial need for wood filler products with comparable performance but which do not use cellulose nitrate. Although cellulose acetate butyrate and cellulose acetate propionate are possible replacements, their costs make them less desirable for wood fillers. Accordingly, the needs exists for cost-effective wood filler compositions that are capable of adhering to a variety of substrate types, including treated and untreated wood, but that do not have the flammability concern of prior wood filler compositions.